Shrouded gas burners and jets therefor

ABSTRACT

A shrouded gas burner which can be used for all gases and in particular natural gas at operating pressures of 6-10 inches water gauge. In all the burners described an array of closely spaced diverging flames is produced which coalesce over a part of their length only thereby achieving both mutual stabilization and satisfactory aeration of the flames as a whole. The use of a shroud around the coalesced region of the flames protects them from direct airflow and contains the products of combustion near to the reaction zone so that they may be reentrained thereby accelerating the combustion process.

United States Patent Inventors John Hancock Leeds; Albert Westerman,Normanton, both of England Appl. No. 846,832

Filed Aug. 1, 1969 Patented Dec. 28, 1971 Assignee Geo. Bray 8: CompanyLimited Leeds, England Priority Aug. 20, 1968 Great Britain 39,712/68SIIROUDED GAS BURNERS AND JETS THEREFOR 15 Claims, 20 Drawing Figs.

US. Cl 431/353, 431/350, 239/499 Int. Cl. F2311 15/02 Field of Search431/350, 353; 239/499 Primary Examiner-Carroll B. Dority, Jr.Attorney-Holcombe, Wetherill & Brisebois ABSTRACT: A shrouded gas burnerwhich can be used for all gases and in particular natural gas atoperating pressures of 6-10 inches water gauge. in all the burnersdescribed an array of closely spaced diverging flames is produced whichcoalesce over a part of their length only thereby achieving both mutualstabilization and satisfactory aeration of the flames as a whole. Theuse of a shroud around the coalesced region of the flames protects themfrom direct airflow and contains the products of combustion near to thereaction zone so that they may be reentrained thereby accelerating thecombustion process.

PATENTED DEC28197I 31530549 sum 2 [IF 5 PATENTED UEB28 l97l 3330.549

SHEET u 0F 5 SI'IROUDED GAS BURNERS AND JETS THEREFOR This inventionrelates to shrouded gas burners for use with gases having differentcompositions and qualities, and in particular to the construction of agas burner which provides stable nonaerated flames with natural gas atoperating pressures of approximately 6-10 inches water gauge.

According to the present invention a shrouded burner includes incombination a gas-jet having a plurality of gas orifices producing, inuse, diverging flames which coalesce only in the region of the gasorifices, and a shroud having at least one wall, said at least one wallprotecting the gas orifices from direct airflow and being shapeddimensioned so that a given flame passes in close proximity to theperipheral edge thereof, said peripheral edge being contoured so thatthe maximum design gas pressure the point of divergence of adjacentflames is level with said edge and at minimum design gas pressure thepoint of divergence of adjacent flames is slightly below said edge.

By arranging for coalescence of the flames in the region of the gasorifices mutual stabilization of the flames is ensured. The shroud andits particular shaping effectively protects the coalesced region fromthe upward movement of air produced by convection currents and therebyfurther enhances flame stability. Consequently, flame lift is preventedeven when natural gas is utilized at operating pressures of up to 10inches water gauge.

Further, by producing diverging flames which coalesce over a part oftheir length only both mutual stabilization and satisfactory aeration ofthe flames is achieved. The divergence of the flames and also the factthat each of them is arranged to pass in close proximity to the lip ofthe shroud also helps flame stabilityby the formation of a current ofair which passes between the gap formed between the flames and the lipof the shroud. This current of air is in a direction counter to theupward velocity of the gas flow and consequently the latter iseffectively reduced, whilst the products of combustion will be retainedin the gap formed between the flames and the walls of the shroud wherethey recirculate. Furthermore, in the case of a cluster of flames or afinal closed ring of flame the divergence of the flames will help tocontain the products of incomplete combustion within the cluster orring.

The invention will now be described in more detail, by way of example,with reference to the accompanying drawings of which;

FIG. 1 shows a diagrammatic plan view of a first jet;

FIG. 2 shows a section taken on the line A-A of FIG. 1;

FIG. 3 shows a section on the line 8-8 of FIG. 1;

FIGS. 4 and 5 show diagrammatic part sectional side and end viewsrespectively of a shrouded burner incorporating the jet shown in FIGS. 1to 3, and illustrate the flame shape and airflow pattern obtained;

FIG. 6 shows a diagrammatic plan view of asecond jet;

FIG. 7 shows a section taken on the line CC of FIG. 6;

FIG. 8 shows a diagrammatic part sectional view respectively of ashrouded burner incorporating the jet shown in FIGS. 6 and 7, andillustrate the flame shape and airflow pattern obtained;

FIG. 9 shows a diagrammatic plan view of a third jet;

FIG. 10 shows a section on the line D-D of FIG. 9;

FIGS 11 and 12 show diagrammatic part sectional side and end viewsrespectively of a shrouded burner incorporating the jet shown in FIGS. 9and I0, and illustrate the flame shape and airflow pattern obtained;

FIG. 13 shows a diagrammatic plan view of the burner illustrated inFIGS. 11 and 12;

FIG. I4 shows a diagrammatic plan view of a fourth jet;

FIG. 15 shows a section on the line E-E of FIG. 14;

FIGS. 16 and 17 show diagrammatic part sectional side and end viewsrespectively of a shrouded burner incorporating the jet shown in FIGS.14 and I5 and illustrate the flame shape and airflow pattern obtained;

FIGS. 18 shows a diagrammatic plan view of the burner illustrated inFIGS. I6 and 17; and

FIGS. 19 and 20 are axial sectional and plan views respectivelyillustrating yet another embodiment of the invention.

Referring to FIGS. 1 to 3, a ceramic or metal gas jet indicatedgenerally at 1 has a spherical projection 2'in which are formed eightorifices 3, 4. The orifices 3, 4 are circular and are. normal to theexternal surface of the jet, that is their origin is the center of thesphere in which they are formed. The set of orifices 3 are formed in oneof two planes (one of which, A- A is shown in FIG. 1) each of which isat an angle of l0-20 from the plane X-X, which is the major axis of thefinal flame which is in the form of a closed elliptical ring, and theset of orifices 4 are formed in one of two planes (one of which B-B isshown in FIG. 1) each of which is at an angle of 40-60 from the planeX--X. In FIG. 2, which is a section through A-A, the orifices 3 areinclined at 3040 to the longitudinal axis of the jet and in FIG. 3, asection through 8-8, the orifices4 are at I520 to the longitudinal axisof the jet. Although in the gas jet illustrated in FIGS. 1 to 3 the twosets of orifices 3, 4 have the same common point of intersection on thelongitudinal axis of the jet it is quite possible for each set oforifices to have a different point of intersection on this axis.

A complete shrouded burner incorporating the jet illustrated in FIGS. 1to 3, is shown in FIGS. 4 and 5. The jet is mounted into a metal socket5 which is provided with an annular shoulder 6 for receiving a shroud 7.The vertical distance of the orifices below the highest point of .theshroud are of the order of 0.4 inch for orifices of 0.010 inch to 0.015inch diameter and for the angles of divergence stated above.

It will be seen from FIGS. 4 and 5 that air flows over the lip of theshroud and between the divergent flames into the center of the coalescedregion 9 and takes up the flow pattern illustrated by the arrows. Thewall of the shroud 7 is at an angle to the longitudinal or vertical axisof the jet so that each flame passes in close proximity to theperipheral edge thereof. A certain amount of air flows over the lip ofthe shroud and down the inside of wall before being taken up by theellipticalflame ring, the clearance between the flames and the lipcontrolling the amount of airflow. The dimensions of the cavity 10,which is of generally wedge-shaped section, formed between the flamesand the wall of the shroud is also of importance since it is in thisarea that recirculation of the products of incomplete combustion occursand the volume of the latter have to be related to the volume of thecavity for purposes of stabilization.

For the particular construction described the internal diameter of theshroud around the jet is 0.30 inch, the internal width at the top in theminor axis is 0.45 inch, and the internal length at the top in the majoraxis is 0.84 inch. The jet can be used with natural gas without flamelift at pressures of up to 12 inches water gauge and has well aeratedflames.

The jet-described above produces a final flame shape which covers agenerally elliptical area in plan view but for some applications, suchas water heaters and central heating boilers which have open combustionchambers, a circular area is required. A preferred form of jet giving afinal flame which is substantially circular in plan view, is illustratedin FIGS. 6 to 8. Four 0.0l3-inch diameter circular orifices 11 areformed in the hemispherical portion 12, of a jet 13. The portion 12 hasan external radius of 0.105 inch and the angles between the longitudinalaxis of adjacent orifices is 24 The angle between the longitudinal axisof each orifice and the longitudinal axis of the jet is 17. FIG. 8illustrates thejet 13 mounted on a metal socket 14 provided with anannular projection 15 for receiving a shroud I6. The latter takes theform of an inverted truncated cone with an internal diameter around thejet of 0.30 inch, an internal diameter at the top of 0.55 inch, the topof the shroud being 0.40 inch above the apex of the jet. Jets with up to12 orifices can be designed to produce circular plan flames. In generalterms, it is desirable that the angle between the longitudinal axes ofadjacent orifices falls between 20 and 30. In order to satisfy thiscondition, the angle between the longitudinal axis of each orifice andthe longitudinal axis of the jet has to be in the range of 10 to 45dependent upon the number of orifices used and their angle ofdivergence.

FIG. 8 shows the final flow pattern, indicated by arrows, and flameformation achieved by the shrouded burner. It will be seen that theburner again produces a coalesced flame portion and that reverse airflowis obtained between the flames themselves and between the flames and theperipheral edge of the wall of the shroud.

ln some applications, particularly gas fires in which the jet fires intobox-type ceramic radiants of rectangular section, a thin flame isrequired in order to avoid flame impingement with consequent poorcombustion or sooting. A jet 18 which produces a thin flame is shown inFIGS. 9 and 10, and has five orifices 19, the three inner ones being of0.0125 inch diameter, and the two outer ones being of 0.0095 inchdiameter,

formed in a single row across the central plane of a sphericalprojection 20. In one example, the external radius of the projection 20is 0.1 10 inch and the angle between the longitudinal axes of adjacentorifices is 17. FIGS 11 to 13 illustrate the jet 18 mounted for a metalsocket 21 provided with an annular projection 22 for receiving a shroud23. Because in this case there is no lateral divergence of the flames,the side portions of the wall of the shroud 22 are parallel, as shown,or they may be slightly convergent, in order to regulate the flow of airinto the shroud through the cleance between the lip and the flame and inorder to contain the combustion products near to the flame base. Themaximum width of the mouth of the shroud is 0.312 inch, the length is1.007 inches and the tip of the jet is 0.570 inches below the uppermostpoint of the shroud.

ln another example of this type of jet the five orifices 19 are ofslightly larger diameter, the three inner ones being 0.145 inches andthe two outer ones 0.01 inches. In this case the external radius of theprojection is 0.135 inches. The external radius of the projection 20must be adjusted in accordance with orifice diameter in order tomaintain a fairly constant ratio between orifice diameter and orificecenter spacing. The dimensions of the shroud, for this example are,width of mouth 0.312, length of mouth 1.100 inches and the tip of thejet is 0.570 inches below the uppermost point of the shroud.

In both examples of the jet 18 described the five orifices could all beof equal size or they could all be different since the relativediameters only affect the overall flame shape.

The depth of the shroud 23 is slightly greater in this case because theangle of divergence of the separate flames is less than for the burnersshown in FIGS. 1 to 8, and the actual point of divergence 24 of adjacentflames is therefore somewhat further from the orifices. This lowerdegree of divergence is necessary to give more coalescence near to theflame base and hence more mutual stabilization. FIGS. 11 and 12illustrate the flame formation and the airflow pattern achieved. It willbe seen that reverse airflow still occurs between the outer surface ofthe flames and the lip of the shroud and the products of incompletecombustion are retained for recirculation in the wedge-shaped gap 25formed between the flame and the wall of the shroud.

Other applications require a large plan area to be heated by a smallnumber of jets, or as in the case of a cooker oven, one jet to produceuniform heat over a long surface. These applications require a jet whichgives a wide flame and such a jet 26 is shown in FIGS. 14 and 15. Thejet 26 is provided with a linear or row of 11 orifices 27 of 0.0117inches diameter formed in a spherically contoured projection 28 ofexternal radius 0.093 inches with an angle of 18 between the axes ofadjacent orifices. A complete shrouded burner incorporating the jet 26is shown in FIGS. 16 to 18. The jet is mounted on a metal socket 29provided with an annular shoulder 30 for receiving a shroud indicatedgenerally at 31. The shroud consists of two substantially semicircularparallel walls 32 of 0.687 inches radius and have a separation ofbetween 0.260 inches and 0.312 inches depending on the orifice diameterswhich are approximately 0.0117 inches. The walls may be parallel asshown or slightly convergent and are closed at the bottom by a pair offlat plates 33 which project from the jet at an angle of about 10 belowthe horizontal FIGS. 16 an 1? illustrate the final flame formation andthe airflow pattern depicted by the arrows. The principle of reverseairflow counter to the flow of gas and over the lips of the walls of theshroud again applies with the products of combustion being retained forrecirculation in the wedge-shaped gaps 35 formed between the flame andthe walls of the shroud. Where a still higher heat concentration isrequired a modified jet, now shown, of the same general form as the jet26 can be used with a double row of orifices with an angle of 24 betweenthe longitudinal axes of the orifices in each row with the shroudsuitably modified, and with the angles of divergence between thelongitudinal axes of the adjacent orifices increased to 25 to allowairflow between the two rows of flame.

A further development, which is not illustrated, is to have 20 0.012inches diameter orifices around the circumference of a jet of 0.18inches diameter with an angle of 18 between the axes of adjacentorifices and with these axes at to the axis of the jet, so that allflames project horizontally from the jet. A circular disc 1.25 inchesdiameter is positioned below the onfices and another above the orificeswith the surfaces of both flaring away from the jet at angles of 15below and above the horizontal respectively.

It will be understood that the orifice dimensions of the variousembodiments described above can be modified where necessary. As theorifices are reduced in size, the rate of flow of gas will decrease aswill the volume of combustion products produced on ignition, and hencefor the purpose of mutual stabilization the orifice spacing has to bereduced. Conversely, with larger orifices, the orifice spacing has to beincreased. Furthemtore, it will be understood that the orifices for eachjet described may all be the same size or they may be all different,change in orifice dimensions only affecting flame length and henceoverall flame shape. Moreover, the number of orifices and theirdisposition one to another can be varied in order to obtain differentoverall flame shapes. The induced air flow and the volume of thecombustion products vary according to on'fice diameter and the flow ofgas therefrom and consequently the dimensions of the jets and shroudsmust be varied correspondingly. The longitudinal axes of all theorifices or sets of orifices of each embodiment described above divergefrom a common origin. However, diverging flames can also be obtained byhaving orifices with parallel axes formed in a thin section or diaphragmas illustrated in FIGS. 19 and 20. The jet has a cylindrical wall 40surmounted by a frustum of a cone 41, the orifices 42 being formed inthe conical surface and being arranged parallel to the axis of the jet.The angle at which the flames leave the jet can be altered by alteringthe thickness of the conical or diaphragm portion. This method ofmanufacture of jets would be particularly applicable to the jetillustrated in FIGS. 6 and 7.

In all the embodiments described above the top or lip of the shroud iscontoured so that at maximum design gas pressure the point of divergenceof adjacent flames is level with the lip, and that at minimum design gaspressure the pint of divergence is slightly below the level of the lip.With this arrangement the burners provide stable nonaerated flames withnatural gas at operating pressures of approximately 6-10 inches watergauge.

In all the embodiments described above the dimensions specified arethose which produce stable flames with methane at operating pressures ofbetween 6 and 10 inches water gauge. There are several forms of naturalgas containing methane, however, with various heating values and thereare also various possible substitute gases which can be used in anemergency. Consequently some tolerance on all the dimensions specifiedis required, and it is suggested that a figure of i 25 percent is notunreasonable.

ln all the burners described the production of closely spaced divergingflames which coalesce over a part of their length only, achieves bothmutual stabilization and satisfactory aeration of the flames as a whole.Furthermore, the divergence of the flames also induces reverse airflowwhich assists ignition, and with a cluster or closed ring of flameshelps to contain the combustion products within the cluster.Furthermore, the use of a shroud or cup around the coalesced region ofthe flames protects them from direct airflow and contains the productsof combustion near to the reaction zone so that they may be reentrainedthereby accelerating the combustion process.

Various forms of jets and burners have been described but it will beevident that other designs based upon the principles listed in theforegoing paragraph are possible. There is also no reason why theseprinciples should not be applied in the design of so-called ribbonburners, for example, in which orifices may be formed in projections onthe upper face of a continuous channel member, and a shroud of sectionappropriate to the required flame shape is placed around eachprojection. Furthermore, the jets described can also be used in thedesign of aerated burners in which case the orifices would have to berather larger to allow for the increased flow arising from premixing ofair with the gas before it issues from the orifices.

We claim:

1. A shrouded burner including in combination a gas jet having aplurality of gas orifices lying on a common ellipse producing, in use,diverging flames which coalesce only in the region of the gas orifices,and a shroud having at least one wall, said at least one wall protectingthe gas'orifices from direct airflow and being shaped and dimensioned sothat a given flame passes in close proximity to the peripheral edgethereof, said peripheral edge being contoured so that at the maximumdesign gas pressure the point of divergence of adjacent flames is levelwith said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.

2. A burner as claimed in claim 11 in which the walls of the shroud aregenerally elliptical.

3. A burner as claimed in claim 2 in which two sets of orifices areprovided the longitudinal axes of the orifices in each set having aditferent common point of intersection on the longitudinal axis of thejet.

4. A shrouded burner for providing stable nonaerated flames with naturalgas at operating pressures of approximately 6 to 10 inches water gaugeincluding in combination a gas jet having a plurality of gas orificesproducing, in use, diverging flames which coalesce only in the region ofthe gas orifices, and a shroud for protecting the gas orifices fromdirect airflow in which:

two sets of orifices are provided which lie on a common ellipse andwhich have diameters of 0.010 inches to 0.015 inches, the longitudinalaxis of each orifice of one of the sets lying at an angle of the orderof to to the 1on gitudinal axis of the jet, and the longitudinal axis ofeach orifice of the other of the sets lying at an angle of the order of30 to 40 to the longitudinal axis of thejet and in which the walls ofthe shroud are generally elliptical, the shroud having an internaldiameter around the jet of the order of 0.30 inches (5 percent), aninternal wid h at the top in the minor axis of the order to 0.45 inch (5percent), and an internal length at the top in the major axis of theorder of 0.84 inch (5 percent), the distance of the orifices below thehighest point of the shroud being of the order of 0.40 inch (5 percent),whereby a given flame passes in close proximity to the peripheral edgeof the shroud, and whereby at the maximum design gas pressure the pointof divergence of adjacent flames is level with said edge, and at minimumdesign gas pressure the point of divergence of adjacent flames isslightly below said edge.

5. A shrouded burner for providing stable nonaerated flames with naturalgas at operating pressures of approximately 6 to 10 inches water gaugeincluding in combination a gas jet having a plurality of gas orificesproducing, in use, diverging flames which coalesce only in the region ofthe gas orifices, and a shroud protecting the gas orifices from directairflow in which:

the orifices lie on a common circle and have diameters of the order of0.013 inch (5 percent), the angle between the longitudinal axis ofadjacent orifices being of the order of 20 to 30 and that between thelongitudinal axis of each orifice and the longitudinal axis of the jetbeing of the order of 10 to 45, and in which the shroud is in the formof an inverted truncated cone the shroud having'an internal diameteraround the jet of the order of 0.30 inch (5 percent) and an internaldiameter at the top of the order of 0.55 inch (5 percent), the distanceof the orifices below the highest point of the shroud being of the orderof 0.40 inch (5 percent), whereby a given flame passes in closeproximity to the peripheral edge of the shroud and whereby at themaximum design gas pressure the point of divergence of adjacent flamesis level with said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.

6. A shrouded burner for providing stable nonaerated flames with naturalgas at operating pressures of approximately 6 to 10 inches water gaugeincluding in combination a gas jet having a plurality of gas orificesproducing, in use, diverging flames which coalesce only in the region ofthe gas orifices, and a tubular shroud for protecting the gas orificesfrom direct airflow in which:

the orifices line in common plane containing the longitudinal axis ofthe jet and have diameters of 0.0095 inch to 0.0145 inch (5 percent),the angle between the longitudinal axis of adjacent orifices being ofthe order of 17, and in which a pair of opposed walls of the shroud aresubstantially planar in configuration, the walls being parallel orslightly upwardly convergent with respect to the longitudinal planecontaining the orifices, the maximum width of the mouth of the shroudbeing of the order of 0.312 inch (5 percent), the length of the mouthbeing of the order of 1.077 inch to 1.100 inch (5 percent), and the tipof the jet being of the order of 0.570 inch (5 percent) below theuppermost point of the shroud, whereby a given flame passes in closeproximity to the peripheral edge of the shroud and whereby at themaximum design gas pressure the point of divergence of adjacent flamesis level with said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.

7. A shrouded burner as claimed in claim 6 in which: there are fiveorifices, the three inner orifices having a diameter of the order of0.0125 inch (5 percent) and the two outer orifices having a diameter ofthe order of 0.0095 inch (5 percent).

8. A shrouded burner as claimed in claim 6 in which:

there are five orifices, the three inner orifices having a diameter ofthe order of 0.0145 inch (5 percent) and the 'two outer orifices havinga diameter of the order of 0.01 15 inch (5 percent).

9. A shrouded burner for providing stable nonaerated flames with naturalgas at operating pressures of approximately 6 to 10 inches water gaugeincluding in combination a gas jet having a plurality of gas orificesproducing, in use, diverging flames which coalesce only in the region ofthe gas orifices, and a shroud for protecting the gas orifices fromdirect airflow, in which:

the orifices lie in a common plane containing the longitudinal axis ofthe jet and have diameters of the order of 0.0117 inch (5 percent), theangle between the longitudinal axis of adjacent orifices being of theorder of 18 and in which the shroud consists of two substantiallysemicircular substantially parallel walls of the order of 0.687 inch (5percent) radius and having a separation of the order of between 0.260and 0.312 inch (5 percent), whereby a given flame passes in closeproximity to the peripheral edges of said walls and whereby at themaximum design gas pressure the point of divergence of adjacent flamesis level with said edges and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.

10. A shrouded burner as claimed in claim 9 in which:

the walls are closed at the bottom by a pair of flat plates whichproject from the jet at an angle of about 10 below the horizontal.

11. A shrouded burner including in combination a gas jet having acylindrical wall surmounted by a frustum of a cone, a plurality of gasorifices being formed in the conical surface and being arranged parallelto the longitudinal axis of the jet so as to produce, in use, divergingflames which coalesce only in the region of the gas orifices, and ashroud having at least one wall, said at least one wall protecting thegas orifices from direct airflow and being shaped and dimensioned sothat a given flame passes in close proximity to the peripheral edgethereof, said peripheral edge being contoured so that at the maximumdesign gas pressure the point of divergence of adjacent flames is levelwith said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.

12. A shrouded burner including in combination a gas jet having aplurality of gas orifices lying in a common plane containing thelongitudinal axis of the jet and producing, in use, diverging flameswhich coalesce only in the region of the gas orifices, and a shroudhaving at least one wall, said at least one wall protecting the gasorifices from direct airflow and being shaped and dimensioned so that agiven flame passes in close proximity to the peripheral edge thereof,said peripheral edge being contoured so that at the maximum design gaspressure the point of divergence of adjacent flames is level with saidedge and at minimum design gas pressure the point of divergence ofadjacent flames is slightly below said edge.

13. A burner as claimed in claim 12 in which sald shroud has a pair ofopposed walls, said walls being substantially planar in configurationand being parallel or slightly upwardly convergent with respect to thelongitudinal plane containing the orifices.

14. A burner as claimed in claim 12 in which the shroud consists of twosubstantially semicircular plane walls, said walls being parallel orslightly upwardly convergent with respect to the longitudinal planecontaining the orifices.

15. A burner as claimed in claim 14 in which the walls are closed at thebottom by a pair of flat plates.

I k i i 1 Disclaimer 3,630,649.John Hancock, Leeds, and AlbertWestewman, Normanton, England. SHROUDED GAS BURNERS AND JETS THEREFOR.Patent dated Dec. 28, 1971. Disclaimer filed May 4:, 1971, by theassignee, Geo. Bray de Company Limited.

Hereby disclaims the portion of the term of the patent subsequent toApr. 22 1986.

[Ofiioial Gazette Apm'l 18, 1972.

1. A shrouded burner including in combination a gas jet having aplurality of gas orifices lying on a common ellipse producing, in use,diverging flames which coalesce only in the region of the gas orifices,and a shroud having at least one wall, said at least one wall protectingthe gas orifices from direct airflow and being shaped and dimensioned sothat a given flame passes in close proximity to the peripheral edgethereof, said peripheral edge being contoured so that at the maximumdesign gas pressure the point of divergence of adjacent flames is levelwith said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.
 2. A burneras claimed in claim 1 in which the walls of the shroud are generallyelliptical.
 3. A burner as claimed in claim 2 in which two sets oforifices are provided the longitudinal axes of the orifices in each sethaving a different common point of intersection on the longitudinal axisof the jet.
 4. A shrouded burner for providing stable nonaerated flameswith natural gas at operating pressures of approximately 6 to 10 incheswater gauge including in combination a gas jet having a plurality of gasorifices producing, in use, diverging flames which coalesce only in theregion of the gas orifices, and a shroud for protecting the gas orificesfrom direct airflow in which: two sets of orifices are provided whichlie on a common ellipse and which have diameters of 0.010 inches to0.015 inches, the longitudinal axis of each orifice of one of the setslying at an angle of the order of 15* to 20* to the longitudinal axis ofthe jet, and the longitudinal axis of each orifice of the other of thesets lying at an angle of the order of 30* to 40* to the longitudinalaxis of the jet and in which the walls of the shroud are generallyelliptical, the shroud having an internal diameter around the jet of theorder of 0.30 inches ( + or - 25 percent), an internal width at the topin the minor axis of the order of 0.45 inch ( + or - 25 percent), and aninternal length at the top in the major axis of the order of 0.84 inch( + or - 25 percent), the distance of the orifices below the highestpoint of the shroud being of the order of 0.40 inch ( + or - 25percent), whereby a given flame passes in close proximity to theperipheral edge of the shroud, and whereby at the maximum design gaspressure the point of divergence of adjacent flames is level with saidedge, and at minimum design gas pressure the point of divergence ofadjacent flames is slightly below said edge.
 5. A shrouded burner forproviding stable nonaerated flames with natural gas at operatingpressures of approximately 6 to 10 inches water gauge including incombination a gas jet having a plurality of gas orifices producing, inuse, diverging flames which coalesce only in the region of the gasorifices, and a shroud protecting the gas orifices from direct airflowin which: the orifices lie on a common circle and have diameters of theorder of 0.013 inch ( + or - 25 percent), the angle between thelongitudinal axis of adjacent orifices being of the order of 20* to 30*and that between the longitudinal axis of each orifice and thelongitudinal axis of the jet being of the order of 10* to 45*, and inwhich the shroud is in the form of an inverted truncated cone the shroudhaving an internal diameter around the jet of the order of 0.30 inch ( +or - 25 percent) and an internal diameter at the top of the order of0.55 inch ( + or - 25 percent), the distance of the orifices below thehighest point of the shroud being of the order of 0.40 inch ( + or - 25percent), whereby a given flame passes in close proximity to theperipheral edge of the shroud and whereby at the maximum dEsign gaspressure the point of divergence of adjacent flames is level with saidedge and at minimum design gas pressure the point of divergence ofadjacent flames is slightly below said edge.
 6. A shrouded burner forproviding stable nonaerated flames with natural gas at operatingpressures of approximately 6 to 10 inches water gauge including incombination a gas jet having a plurality of gas orifices producing, inuse, diverging flames which coalesce only in the region of the gasorifices, and a tubular shroud for protecting the gas orifices fromdirect airflow in which: the orifices lie in a common plane containingthe longitudinal axis of the jet and have diameters of 0.0095 inch to0.0145 inch ( + or - 25 percent), the angle between the longitudinalaxis of adjacent orifices being of the order of 17*, and in which a pairof opposed walls of the shroud are substantially planar inconfiguration, the walls being parallel or slightly upwardly convergentwith respect to the longitudinal plane containing the orifices, themaximum width of the mouth of the shroud being of the order of 0.312inch ( + or - 25 percent), the length of the mouth being of the order of1.077 inch to 1.100 inch ( + or - 25 percent), and the tip of the jetbeing of the order of 0.570 inch ( + or - 25 percent) below theuppermost point of the shroud, whereby a given flame passes in closeproximity to the peripheral edge of the shroud and whereby at themaximum design gas pressure the point of divergence of adjacent flamesis level with said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.
 7. A shroudedburner as claimed in claim 6 in which: there are five orifices, thethree inner orifices having a diameter of the order of 0.0125 inch ( +or - 25 percent) and the two outer orifices having a diameter of theorder of 0.0095 inch ( + or - 25 percent).
 8. A shrouded burner asclaimed in claim 6 in which: there are five orifices, the three innerorifices having a diameter of the order of 0.0145 inch ( + or - 25percent) and the two outer orifices having a diameter of the order of0.0115 inch ( + or - 25 percent).
 9. A shrouded burner for providingstable nonaerated flames with natural gas at operating pressures ofapproximately 6 to 10 inches water gauge including in combination a gasjet having a plurality of gas orifices producing, in use, divergingflames which coalesce only in the region of the gas orifices, and ashroud for protecting the gas orifices from direct airflow, in which:the orifices lie in a common plane containing the longitudinal axis ofthe jet and have diameters of the order of 0.0117 inch ( + or - 25percent), the angle between the longitudinal axis of adjacent orificesbeing of the order of 18* and in which the shroud consists of twosubstantially semicircular substantially parallel walls of the order of0.687 inch ( + or - 25 percent) radius and having a separation of theorder of between 0.260 and 0.312 inch ( + or - 25 percent), whereby agiven flame passes in close proximity to the peripheral edges of saidwalls and whereby at the maximum design gas pressure the point ofdivergence of adjacent flames is level with said edges and at minimumdesign gas pressure the point of divergence of adjacent flames isslightly below said edge.
 10. A shrouded burner as claimed in claim 9 inwhich: the walls are closed at the bottom by a pair of flat plates whichproject from the jet at an angle of about 10* below the horizontal. 11.A shrouded burner including in combination a gas jet having acylindrical wall surmounted by a frustum of a cone, a plurality of gasorifices being formed in the conical surface and being arranged parallelto the longitudinal axis of the jet so as to produce, in use, divergingflames whiCh coalesce only in the region of the gas orifices, and ashroud having at least one wall, said at least one wall protecting thegas orifices from direct airflow and being shaped and dimensioned sothat a given flame passes in close proximity to the peripheral edgethereof, said peripheral edge being contoured so that at the maximumdesign gas pressure the point of divergence of adjacent flames is levelwith said edge and at minimum design gas pressure the point ofdivergence of adjacent flames is slightly below said edge.
 12. Ashrouded burner including in combination a gas jet having a plurality ofgas orifices lying in a common plane containing the longitudinal axis ofthe jet and producing, in use, diverging flames which coalesce only inthe region of the gas orifices, and a shroud having at least one wall,said at least one wall protecting the gas orifices from direct airflowand being shaped and dimensioned so that a given flame passes in closeproximity to the peripheral edge thereof, said peripheral edge beingcontoured so that at the maximum design gas pressure the point ofdivergence of adjacent flames is level with said edge and at minimumdesign gas pressure the point of divergence of adjacent flames isslightly below said edge.
 13. A burner as claimed in claim 12 in whichsaId shroud has a pair of opposed walls, said walls being substantiallyplanar in configuration and being parallel or slightly upwardlyconvergent with respect to the longitudinal plane containing theorifices.
 14. A burner as claimed in claim 12 in which the shroudconsists of two substantially semicircular plane walls, said walls beingparallel or slightly upwardly convergent with respect to thelongitudinal plane containing the orifices.
 15. A burner as claimed inclaim 14 in which the walls are closed at the bottom by a pair of flatplates.